The present invention relates to quantum information processing, and more specifically, to a modular design for quantum information processing hardware based on an array of clusters of quantum systems.
Quantum information processing is a new paradigm of information processing where information is stored and processed with systems obeying the laws of quantum mechanics rather than classical mechanics. Such computers have been theoretically shown to be capable of solving important problems using exponentially fewer computational resources (e.g. operations, memory elements) than classical computers. As such, quantum physics provides a basis for achieving computational power to address certain categories of problems that are intractable with current machine computation.
By analogy with classical bits, the fundamental unit of quantum information is called the quantum bit, or qubit. In order to realize quantum information processing tasks, one must develop and implement a physical instantiation of a plurality of quantum bits. These physical instantiations are likewise referred to as quantum bits or qubits. The term ‘qubit’ is thus used in reference to the physical system realizing the instantiation and the unit of quantum information stored therein.
The physical quantum mechanical system realizing the instantiation of a qubit must possess at least two distinct and distinguishable eigenstates in order to represent at least two logic states. Instantiations where the number of distinct and distinguishable eigenstates is greater than two can be likewise used. These additional eigenstates may be explicitly used to represent additional logic states, or otherwise made use of for an information processing task. Specifically, additional eigenstates may be exploited to facilitate measurement of the two eigenstates encoding the two logic states; or to facilitate transformations of the Hilbert space associated to the two eigenstates encoding the two logic states.
Several physical systems and fields of physics have been proposed as potential frameworks and development grounds for quantum information processing. These include, but are not limited to: solid state nuclear spins, measured and controlled electronically or with nuclear magnetic resonance, trapped ions, atoms in optical cavities (cavity quantum-electrodynamics), liquid state nuclear spins, electronic charge or spin degrees of freedom in quantum dots, superconducting quantum circuits based on Josephson junctions and electrons on Helium.
Currently the most active areas of research towards quantum computing are superconducting qubits, trapped ions, trapped atoms, and quantum dots. The largest quantum computer built in any of these systems to date consists of around 10-16 qubits, and most implementations are focused on the demonstration of a specific quantum algorithm or quantum state.
The requirements for building a large-scale quantum computer are more intricate than quantum mechanical properties such as superposition and entanglement alone. There is a set of requirements that must be fulfilled in order to build a practical quantum computer. One requirement is to have a system of qubits that can be initialized to a known state. Another requirement is the ability to manipulate this state by applying single and multi-qubit gate operations such that any arbitrary logic operation can be implemented. Finally, the outcome of the computation must be measured through known techniques. In addition, for a quantum system to retain the delicately created superposition and entangled states for sufficiently long times (i.e., coherence times) it must be well isolated from the environment. However, in order to manipulate the quantum system according to the steps of the desired algorithm it must inherently also be coupled to the external environment thereby introducing noise mechanisms that reduce coherence times.